Electroplating ferrous-base molded bodies



United States Patent ELECTROPLATING FERROUS-BASE MOLDED BODIES Plma Szky, Izidor Nemnyi, and Terezia Eiilliis, Budapest, Hungary, assiguors to Altalanos Gptervezti Iroda, Budapest, Hungary No Drawing. Filed June 13, 1958, Ser. No. 741,720

Claims priority, application Hungary July 12, 1957 2 Claims. (Cl. 204-43) The object of the invention is an iron containing body manufactured by powder metallurgy, which is electroplated in accordance with galvanic action and under the electroplated coating corrosion does not occur. A further object of the invention is a process for electroplating iron containing bodies manufactured by powder metallurgy.

It is often desirable to electroplate molded bodies which were manufactured by powder metallurgy, especially with nickel or nickel and chromium. These bodies having a porous structure the galvanic bath used for the electroplating penetrates into them causing corrosion under the coating which might lead to the disintegration of the bodies. This phenomenon prevents the direct electroplating of such porous bodies.

It has been found that the corrosion mentioned above can be eliminated on these iron containing bodies manufactured by powder metallurgy and a firmly adhering electrodeposit can be achieved if it is applied on a body, the surface of which is provided with a blue oxide layer produced by superheated steam.

It is known in the art to produce a blue oxide layer on the surface of powder metallurgical bodies in order to reduce their porosity, to increase their resistance to corrosion and their hardness. Such blue oxide coatings are produced with superheated steam at a temperature ranging e.g. from 550 to 600 degrees centigrade and gives a certain protection against corrosion. Such bodies were not electroplated because it was not to be believed that the electrodeposit would firmly adhere to such an oxide layer. In the course of our experiments it was found that this blue oxide layer adheres not only to a great extent to the iron containing bodies manufactured by powder metallurgy, but also that a firmly adhering electrodeposit, for instance copper, nickel or chromium, can be produced on it. So for instance a nickel coating adheres so firmly to the blue oxide layer that the intermediate copper layer generally used hithereto is unnecessary, a fact which is surprising.

Iron containing molded bodies manufactured by powder metallurgy, having a pore content more than can be treated according to the invention and firmly adhering electrolytically deposited metal layer can be obtained. The process according to the invention can be used with particular advantage on iron containing bodies, manufactured by powder metallurgy, the porosity of which exceeds and can range up to 30%. The blue oxide layer processed on the surface of these bodies closes the surface pores sufiiciently, so that under the electrolytically deposited metal layer corrosion does not occur.

Example 1 Gears, produced by powder metallurgy from iron powder containing 7% Cu and 0.2% C in a manner known in the art, are treated with superheated steam at a temperature ranging between 550 and 600 degrees centigrade for 20 minutes. A blue oxide layer is formed in the course of this treatment. After cooling, these gears are nickel plated in a galvanic bath, accordingto known practice, for 50 minutes, whereby a nickel coating of 8-1011. is obtained. These nickel electroplated gears are polished with cloth buffs known in the art. This nickel layer can be coated if desired by electrolytically deposited chromium.

Example 2 Gears are manufactured from iron powder containing 30% Cu and Fe, they are coated with a blue oxide layer and electroplated with nickel according to Example 1.

The nickel layer adheres in both cases firmly and the corrosion caused by the galvanic bath under the nickel layer cannot be stated.

The porosity of a nickel coating on such a blue oxide layer is less than that of a nickel coating produced in the usual manner on an electrodeposited copper layer.

Example 3 Molded bodies were produced from iron powder according to the so-called Hametag process with an additive of 1% graphite and 2% copper powder in the usual way known in the art. The porosity of these bodies amounts to about 30%. These bodies are treated for .6 hour with superheated steam at a temperature between 550 and 600 degrees centigrade. Owing to the high porosity, not all the pores .are closed by the blue oxide layer so that some of the galvanic bath penetrates into the pores. But the quantity of this penetrated liquid is so small that the corrosion can practically be neglected. Should the porosity of the molded body produced by powder metallurgy not exceed 20% of the pores on the surface are sufficiently closed by the blue oxide layer applied so that electrolyte does not penetrate into the pores in the course of electroplating and so no corrosion can be traced under the electrolytically deposited layer.

What we claim is:

l. A process for electroplating ferrous-base molded bodies having a porosity ranging between 10 and 30% manufactured by powder metallurgy, comprising first providing the bodies with a blue oxide layer by treatment with superheated steam, and, after cooling, electrolytically depositing a metal coating on the blue oxide layer.

2. A process according to claim 1, in which the metal coating is a nickel coating.

References Cited in the file of this patent UNITED STATES PATENTS 2,528,717 H Batcheller Nov. 7, 1950 

1. A PROCESS FOR ELECTROPLATING FERROUS-BASE MOLDED BODIES HAVING A POROSITY RANGING BETWEEN 10 AND 30% MANUFACTURED BY POWDER METALLURGY, COMPRISING FIRST PROVIDING THE BODIES WITH A BLUE OXIDE LAYER BY TREATMENT WITH SUPERHEATED STEAM, AND, AFTER COOLING, ELECTROLYTICALLY DEPOSITING A METAL COATING ON THE BLUE OXIDE LAYER. 